U.S. patent application number 15/048917 was filed with the patent office on 2017-08-24 for waveguide pupil relay.
The applicant listed for this patent is Tuomas Heikki Sakari Vallius, Richard Andrew Wall. Invention is credited to Tuomas Heikki Sakari Vallius, Richard Andrew Wall.
Application Number | 20170242249 15/048917 |
Document ID | / |
Family ID | 58213327 |
Filed Date | 2017-08-24 |
United States Patent
Application |
20170242249 |
Kind Code |
A1 |
Wall; Richard Andrew ; et
al. |
August 24, 2017 |
Waveguide Pupil Relay
Abstract
A waveguide-based pupil relay for an optical system can comprise
a light-transmissive substrate that includes a plurality of
internally reflective surfaces to enable light rays of a plurality
of different colors to propagate through the substrate by total
internal reflection. The pupil relay can further include an input
surface to input light rays of the plurality of different colors
through an entry pupil of the optical waveguide, and an output
surface to output light rays of the plurality of different colors
from the substrate through an exit pupil of the optical waveguide.
The pupil relay can have optical properties such that the entry
pupil and exit pupil have substantially identical size and shape
and such that the input light rays and output light rays have
substantially identical chromatic properties.
Inventors: |
Wall; Richard Andrew;
(Kirkland, WA) ; Vallius; Tuomas Heikki Sakari;
(Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wall; Richard Andrew
Vallius; Tuomas Heikki Sakari |
Kirkland
Espoo |
WA |
US
FI |
|
|
Family ID: |
58213327 |
Appl. No.: |
15/048917 |
Filed: |
February 19, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/0016 20130101;
G02B 27/0176 20130101; G02B 6/0031 20130101; G02B 6/0055 20130101;
G02B 2027/015 20130101; G02B 2027/0116 20130101; G02B 27/0172
20130101 |
International
Class: |
G02B 27/01 20060101
G02B027/01; F21V 8/00 20060101 F21V008/00 |
Claims
1. An optical waveguide comprising: a light-transmissive substrate
that includes a plurality of internally reflective surfaces to
enable light rays of a plurality of different colors to propagate
through the substrate by total internal reflection; an input
surface to input light rays of the plurality of different colors
through an entry pupil of the optical waveguide; and an output
surface to output light rays of the plurality of different colors
from the substrate through an exit pupil of the optical waveguide,
the optical waveguide having optical properties such that the entry
pupil and exit pupil have substantially identical size and shape
and such that the input light rays and output light rays have
substantially identical chromatic properties.
2. The optical waveguide of claim 1, wherein the substrate is
rigid.
3. The optical waveguide of claim 1, the optical waveguide having
physical dimensions such that the optical waveguide is suitable for
use in a near-eye display device.
4. The optical waveguide of claim 1, the optical waveguide having
optical characteristics such that the light rays of the plurality
of different colors propagate collinearly through the waveguide
substrate.
5. The optical waveguide of claim 1, the optical waveguide having
optical characteristics such that the light rays of at least some
of the plurality of different colors propagate non-collinearly
through the waveguide substrate.
6. The optical waveguide of claim 1, wherein the plurality of
different colors include at least three colors of a primary color
model.
7. The optical waveguide of claim 1, wherein at least one of the
input surface or the output surface is oriented at an oblique angle
relative to the plurality of internally reflective surfaces.
8. The optical waveguide of claim 7, wherein the input surface is
oriented at an oblique angle relative to the plurality of
internally reflective surfaces.
9. The optical waveguide of claim 7, wherein each of the input
surface and the output surface is oriented at an oblique angle
relative to the plurality of internally reflective surfaces.
10. The optical waveguide of claim 1, wherein the optical waveguide
comprises a first wedge-shaped prism coupled to an input end of the
substrate, and wherein the input surface is a first surface of the
first wedge-shaped prism.
11. The optical waveguide of claim 10, wherein: the input surface
is oriented at a first oblique angle relative to the plurality of
internally reflective surfaces; and the first wedge-shaped prism
has a second surface oriented at a second oblique angle relative to
the plurality of internally reflective surfaces, wherein the second
oblique angle is different from the first oblique angle.
12. The optical waveguide of claim 10, wherein the optical
waveguide comprises a second wedge-shaped prism coupled to an
output end of the substrate, and wherein the output surface is a
first surface of the second wedge-shaped prism.
13. The optical waveguide of claim 1, wherein the substrate
includes a plurality of internally reflective surfaces to cause the
light of the plurality of colors to propagate through the substrate
by total internal reflection, and wherein the input surface and the
output surface are each substantially coplanar with at least one of
the plurality of internally reflective surfaces.
14. The optical waveguide of claim 1, comprising a diffraction
element that is part of the substrate and located on or proximate
to the input surface to cause the light rays of the plurality of
different colors to propagate collinearly through the
substrate.
15. The optical waveguide of claim 1, comprising a diffraction
element that is part of the substrate and located on or proximate
to the output surface to cause the light rays of the plurality of
different colors to be out-coupled collinearly from the optical
waveguide.
16. The optical waveguide of claim 1, comprising a diffraction
element that is part of the substrate and located on or proximate
to a surface of the substrate between the input surface and the
output surface, the diffraction element configured to cause light
rays of at least one the plurality of different colors to be
out-coupled from the optical waveguide at an intermediate location
on the substrate between the input surface and the output
surface.
17. The optical waveguide of claim 1, comprising a plurality of
diffraction elements that are part of the substrate and located on
or proximate to the input surface or the output surface, each of
the diffraction gratings being configured to transmit light of a
different color.
18. The optical waveguide of claim 17, wherein at least one the
plurality of diffraction elements comprises a plurality of stacked
diffraction elements.
19. A pupil relay comprising: a rigid, light-transmissive waveguide
capable of conveying light rays of a plurality of different colors;
and means for propagating the light rays of a plurality of
different colors through the waveguide such that an exit pupil of
the pupil relay has substantially identical size and shape as an
entry pupil of the pupil relay and such that light rays input to
the entry pupil and light rays output through the exit pupil have
substantially identical chromatic properties.
20. A near-eye display device comprising: a light source; a
microdisplay imager optically coupled to receive light from the
light source; a first waveguide having an optical input port and an
optical output port, the optical output port being disposed to
output light to a light receptor of a user of the near-eye display
device; and a second waveguide optically coupled to convey the
light from the microdisplay imager to the input port of the first
waveguide, the second waveguide including a light-transmissive
substrate that includes a plurality of internally reflective
surfaces to enable light rays of a plurality of different colors to
propagate through the substrate by total internal reflection; an
input surface to input, through an entry pupil of the second
waveguide, input light rays of the plurality of different colors;
and an output surface to output light rays of the plurality of
different colors from the substrate through an exit pupil of the
optical waveguide, the second waveguide having optical properties
such that the entry pupil and exit pupil have substantially
identical size and shape and such that the input light rays and
output light rays have substantially identical chromatic
properties.
Description
BACKGROUND
[0001] A pupil relay system is used to spatially translate a pupil
from one position to another in an optical system. Though a pupil
relay system can be modeled with ideal paraxial lenses in optical
design software, practical pupil relay systems such as the
Offner-type relay tend to be very complex to correct for
aberrations in the system and to ensure that the performance of the
system does not degrade with that of the pupil relay. With their
relatively large size and weight, the design of conventional pupil
relays makes them poorly suited for use in head-mounted display
(HMD) systems and other near-eye display systems. In addition,
tolerances on these optical systems are usually too sensitive to
permit mass-production of any included pupil relay in a
cost-effective manner.
SUMMARY
[0002] Introduced here are at least one apparatus and at least one
method (collectively and individually, "the technique introduced
here" or simply "the technique") to spatially translate a pupil
from one position to another in an optical system. The technique
enables a pupil relay to be mass-produced in a cost-effective
manner while complying with extremely tight tolerances.
[0003] In some embodiments the technique includes an optical
waveguide comprising a light-transmissive substrate that includes a
plurality of internally reflective surfaces to enable light rays of
a plurality of different colors to propagate through the substrate
by total internal reflection. The optical waveguide can further
include an input surface to input light rays of the plurality of
different colors through an entry pupil of the optical waveguide,
and an output surface to output light rays of the plurality of
different colors from the substrate through an exit pupil of the
optical waveguide. The optical waveguide can have optical
properties such that the entry pupil and exit pupil have
substantially identical size and shape and such that the input
light rays and output light rays have substantially identical
chromatic properties.
[0004] In certain embodiments the technique may be implemented in a
near-eye display device, such as an HMD device. In certain
embodiments the technique may be implemented in conjunction with a
technique for increasing the field of view (FOV) of displayed
images in a display device, such as an HMD device.
[0005] Other aspects of the technique will be apparent from the
accompanying figures and detailed description.
[0006] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used to limit the scope of the claimed
subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] One or more embodiments of the present disclosure are
illustrated by way of example and not limitation in the figures of
the accompanying drawings, in which like references indicate
similar elements.
[0008] FIG. 1 shows an example of an HMD device that may
incorporate the technique introduced herein.
[0009] FIG. 2A shows a right side view of display components that
may be contained within the HMD device of FIG. 1.
[0010] FIG. 2B shows a front view of display components that may be
contained within the HMD device of FIG. 1.
[0011] FIG. 3 shows a single input pupil waveguide to convey light
to a particular eye of the user.
[0012] FIG. 4 shows a multiple input pupil waveguide to convey
light to a particular eye of the user.
[0013] FIG. 5 schematically shows an example of relevant components
of the display module for one eye of the user, usable in connection
with the multiple input pupil waveguide in FIG. 4.
[0014] FIG. 6 schematically shows an example of relevant components
of the display module for one eye of the user, usable in connection
with the multiple input pupil waveguide in FIG. 4, for an
embodiment that uses a light engine containing multiple
imagers.
[0015] FIG. 7 schematically illustrates an example of relevant
components of the light engine of FIG. 6.
[0016] FIG. 8 illustrates an example of a method of using multiple
input pupils on a waveguide in an HMD device.
[0017] FIG. 9A illustrates a waveguide pupil relay with faceted
ends.
[0018] FIG. 9B illustrates a zoomed view of the input end of the
waveguide pupil relay of FIG. 9A.
[0019] FIG. 9C illustrates a zoomed view of the output end of the
waveguide pupil relay of FIG. 9A.
[0020] FIG. 10 illustrates a waveguide pupil relay that includes
diffractive optical elements (DOEs) according to a first
embodiment.
[0021] FIG. 11 illustrates a waveguide pupil relay that includes
DOEs according to a second embodiment.
[0022] FIG. 12 illustrates a waveguide pupil relay that includes a
DOE positioned intermediately along a length of the waveguide to
out-couple light, according to a first embodiment.
[0023] FIG. 13 illustrates a waveguide pupil relay that includes a
DOE positioned intermediately along a length of the waveguide to
out-couple light, according to a second embodiment.
DETAILED DESCRIPTION
[0024] In this description, references to "an embodiment", "one
embodiment" or the like, mean that the particular feature,
function, structure or characteristic being described is included
in at least one embodiment of the technique introduced here.
Occurrences of such phrases in this specification do not
necessarily all refer to the same embodiment. On the other hand,
the embodiments referred to also are not necessarily mutually
exclusive.
[0025] The following description generally assumes that the "user"
of a display device is a human, to facilitate description. Note,
however, that a display device embodying the technique introduced
here can potentially be used by a user that is not human, such as a
machine or an animal. Hence, the term "user" herein can refer to
any of those possibilities, except as may be otherwise stated or
evident from the context. Further, the term "optical receptor" is
used herein as a general term to refer to a human eye, an animal
eye, or a machine-implemented optical sensor designed to detect an
image in a manner analogous to a human eye.
[0026] Some artificial reality (AR) enabled HMD devices include one
or more transparent waveguides arranged so that they are positioned
to be located directly in front of each eye of the user when the
HMD device is worn by the user, to project light representing
generated images into the eye of the user. With such a
configuration, images generated by the HMD device can be overlaid
on the user's view of the real world. The FOV of such an HMD
display device may be limited, however, by the refractive index of
the materials used to make the waveguides. This constraint can be
mitigated by providing two or more input pupils/in-coupling
elements on the waveguide for each eye of the user, which enables a
significantly larger FOV to be achieved with currently available
materials and manufacturing technology.
[0027] One way to accommodate the use of two or more in-coupling
elements/pupils on a waveguide (per eye) would be to use two or
more corresponding light engines for each eye. A light engine is a
component assembly that includes one or more light sources (e.g.,
red, green and blue light sources), one or more microdisplay
imagers, and associated optics. However, the use of multiple light
engines for each eye increases weight, price and size
significantly, which is undesirable in a small-footprint device
such as an HMD device. Additionally, the mechanical alignment
between multiple light engines is challenging, since the tolerances
tend to be on the order of arc-seconds in order to provide adequate
image quality. Therefore, the use of two light engines on a
waveguide may not be desirable with existing technology.
[0028] The technique introduced here, however, overcomes this
challenge in some embodiments by providing a switchable element in
a light engine, to switch the direction of the image to at least
two different optical paths, and pupil relay optics to transfer the
pupil to another location. The relay optics can be placed after the
switching element to transfer the image further away from the light
engine, to enable larger distances between the in-coupling
elements. This technique, therefore, enables a single light engine
to provide two pupils for the image to two separate input ports on
a waveguide, without significantly increasing the cost and size of
the system, thereby greatly increasing the FOV with current
materials and manufacturing technologies.
[0029] Another approach to solving this problem is to combine two
or more microdisplay imagers in the same light engine. The same
illumination and imaging optics can be used to produce two
overlaying images, which can be separated using, for example, a
polarization mirror. As with the approach mentioned above, pupil
relay optics can be used to transfer any one or more of the pupils
further away from the light engine, to enable the input ports on
the waveguide to be located relatively far away from each other.
Additional details regarding the technique introduced here are
provided below.
[0030] FIG. 1 shows an example of an HMD device in which the
technique introduced here can be incorporated. The HMD device 40
may provide virtual reality (VR) and/or augmented reality (AR)
display modes for the user, i.e., the wearer of the device. To
facilitate description, it is henceforth assumed that the HMD
device 40 is designed for AR visualization.
[0031] In the illustrated embodiment, the HMD device 40 includes a
chassis 41, a transparent protective visor 42 mounted to the
chassis 41, and left and right side arms 44 mounted to the chassis
41. The visor 42 forms a protective enclosure for various display
elements (not shown) that are discussed below.
[0032] The chassis 41 is the mounting structure for the visor 42
and side arms 44, as well as for various sensors and other
components (not shown) that are not germane to this description. A
display assembly (not shown) that can generate images for AR
visualization is also mounted to the chassis 41 and enclosed within
the protective visor 42. The visor assembly 42 and/or chassis 41
may also house electronics (not shown) to control the functionality
of the display assembly and other functions of the HMD device 40.
The HMD device 40 further includes an adjustable headband 45
attached to the chassis 41, by which the HMD device 40 can be worn
on a user's head.
[0033] FIGS. 2A and 2B show, in accordance with certain
embodiments, right side and front orthogonal views, respectively,
of display components that may be contained within the visor 42 of
the HMD device 40. During operation of the HMD device 40, the
display components are positioned relative to the user's left eye
56.sub.L and right eye 56.sub.R as shown. The display components
are mounted to the interior surface of the chassis 41. The chassis
41 is shown in cross-section in FIG. 2A.
[0034] The display components are designed to overlay
three-dimensional images on the user's view of his real-world
environment, e.g., by projecting light into the user's eyes.
Accordingly, the display components include a display module 54
that houses a light engine including components such as: one or
more light sources (e.g., one or more light emitting diodes
(LEDs)); one or more microdisplay imagers, such as liquid crystal
on silicon (LCOS), liquid crystal display (LCD), digital
micromirror device (DMD); and one or more lenses, beam splitters
and/or waveguides. The microdisplay imager(s) (not shown) within
the display module 54 may be connected via a flexible circuit
connector 55 to a printed circuit board 58 that has image
generation/control electronics (not shown) mounted on it.
[0035] The display components further include a transparent
waveguide carrier 51 to which the display module 54 is mounted, and
multiple transparent waveguides 52 stacked on the user's side of
the waveguide carrier 51, for each of the left eye and right eye of
the user. The waveguide carrier 51 has a central nose bridge
portion 110, from which its left and right waveguide mounting
surfaces extend. Multiple waveguides 52 are stacked on each of the
left and right waveguide mounting surfaces of the waveguide carrier
51, to project light emitted from the display module and
representing images into the left eye 56.sub.L and right eye
56.sub.R, respectively, of the user. The display assembly 57 can be
mounted to the chassis 41 through a center tab 50 located at the
top of the waveguide carrier 51 over the central nose bridge
section 110.
[0036] FIG. 3 shows a single input pupil design for a waveguide
that can be mounted on the waveguide carrier 51 to convey light to
a particular eye of the user, in this example, the right eye of
user. A similar waveguide can be designed for the left eye, for
example, as a (horizontal) mirror image of the waveguide shown in
FIG. 3. The waveguide 10 is transparent and, as can be seen from
FIGS. 2A and 2B, would normally be disposed directly in front of
the right eye of the user during operation of the HMD device, e.g.,
as one of the waveguides 52 in FIG. 2A. The waveguide 10 is,
therefore, shown from the user's perspective during operation of
the HMD device 40.
[0037] The waveguide 10 includes a single input port 11 (also
called in-coupling element, and corresponding to the single input
pupil) located in the region of the waveguide 10 that is closest to
the user's nose bridge when the HMD device 40 is worn by the user.
The input port 11 may be formed from, for example, a surface
diffraction grating, volume diffraction grating, or a reflective
component. The waveguide 10 further includes a single output port
13 (also called out-coupling element) and a transmission channel
12. A right-eye output port of the display module (not shown) is
optically coupled (but not necessarily physically coupled) to the
input port 11 of the waveguide 10. During operation, the display
module 54 (not shown) outputs light representing an image for the
right eye from its right-eye output port into the input port 11 of
the waveguide 10.
[0038] The transmission channel 12 conveys light from the input
port 11 to the output port 13 and may be, for example, a surface
diffraction grating, volume diffraction grating, or a reflective
component. The transmission channel 12 may be designed to
accomplish this by use of total internal reflection (TIR). Light
representing the image for the right eye is then projected from the
output port 13 to the user's eye.
[0039] As mentioned above, however, the single input port design
shown in FIG. 3 has a relatively limited FOV. FIG. 4, therefore,
shows a dual-input pupil design for a waveguide, which can be used
instead of the waveguide in FIG. 3 to provide a greater FOV. Note
that while the present disclosure describes waveguides with one or
two input ports/pupils and a single output port/pupil, a display
device incorporating the technique introduced here may have a
waveguide with more than two input ports/pupils and/or more than
one output port/pupil for a given eye. Further, while the example
of FIG. 4 is for the right eye, a similar waveguide can be designed
for the left eye, for example, as a (horizontal) mirror image of
the waveguide in FIG. 4.
[0040] As shown, the waveguide 20 in FIG. 4 includes two separate
input ports 21 and 22, two transmission channels 23 and 24, and an
output port 25. During operation, each of the input ports 21, 22
receives light (from the display module 54) representing a
different portion of the image for the right eye of the user. Each
of the transmission channels 23, 24 is optically coupled to a
separate one of the input ports 21 or 22 and conveys light from
only the corresponding input port 21 or 22 to the output port 25.
Each of the transmission channels 23, 24 may be, for example, an
internal or surface diffraction grating design to channel light by
TIR. Light from the two different portions of the image is combined
at the output port 25 and projected into the eye of the user as a
single integrated image.
[0041] In some embodiments, the left input port 21 receives the
left portion (e.g., half) of the image for one eye of the user
(e.g., the right eye) while the right input port 22 receives the
right portion (e.g., half) of the image for that same eye. Each
portion of the image can include all of the color components that
are present in the complete image, e.g., red, green and blue color
components. The portions of the image may be generated in a tiled
manner, i.e., where they are spatially contiguous and
non-overlapping, or they may at least partially overlap spatially.
Further, in other embodiments, rather than generating left and
right portions of the image, the separate portions of the image
could be upper and lower portions of the image, or the image could
be spatially divided in some other manner. Additionally, the
waveguide 20 could have more than two input ports, in which case
the image could be provided to the waveguide 20 in the form of
three or more separate image portions, which are reintegrated in
the waveguide 20.
[0042] Hence, in at least some embodiments, different portions of
an image for a given eye of the user are generated and input
simultaneously into separate input ports of a waveguide, then
reintegrated within the waveguide and projected into the eye of the
user as a single integrated image, to produce a larger FOV. In
other embodiments, the separate portions of the image could be
input to the waveguide in a time division multiplexed manner,
rather than simultaneously. Further, in some embodiments, the
physical placement of the input ports on the waveguide may be
different from that shown in FIG. 4. For example, the input ports
could be spaced apart vertically on the waveguide rather than, or
in addition to, horizontally. Other input port configurations are
also possible.
[0043] As mentioned above, one possible way to employ a dual input
pupil waveguide, such as shown in FIG. 4, would be to use multiple
light engines, i.e., one light engine for each input pupil.
However, that approach has disadvantages, as discussed above. FIG.
5 illustrates an alternative approach that does not have the
disadvantages of multiple light engines. In particular, FIG. 5
schematically shows an example of certain relevant components of
the display module 54 for one eye of the user (left or right), that
may be used in connection with a dual input pupil waveguide such as
shown in FIG. 4. The view in FIG. 5 is from directly above the
display module 54, looking down.
[0044] In the example of FIG. 5, the display module 54 includes a
light engine 31, an optical switch 32 and a pupil relay 33. Though
not shown, the display module 54 may also include similar or
identical components for the other eye of the user. In some
embodiments, the light engine 31 includes one or more light sources
(not shown), such as one or more colored LEDs. For example, the
light engine 31 can include red, green and blue LEDs to produce the
red, green and blue color components, respectively, of the image.
Additionally, the light engine 31 includes at least one
microdisplay imager (not shown), such as an LCOS imager, LCD or
DMD; and may further include one or more lenses, beam splitters,
waveguides, and/or other optical components (not shown).
[0045] The optical switch 32 controls the propagation direction of
the light output by the light engine 31, representing each
particular portion of the image, to one of two different optical
paths. In the illustrated embodiment, the first path is for the
left half of the image and leads to an output port 34 of the
display module 54 that is coupled to one corresponding input port
21 of the waveguide 20. The other optical path is for the right
portion of the image and includes a pupil relay 33, which
propagates that portion of the image to a second output port 36 of
the display module 54, which is optically coupled to a second
corresponding input port 22 of the waveguide 20.
[0046] The optical switch 32 selectively controls the propagation
direction of light from the light engine 31 based on a switching
criterion, such as polarization. For example, one half of the image
may have s-polarization while the other half of image has
p-polarization, where the optical switch 32 conveys s-polarized
light along one optical path and conveys p-polarized light along
the other optical path. The switch 32 can be, for example, an LCD
mirror that either transmits light or acts as a perfect mirror,
depending on the applied voltage. Note, however, that a switching
criterion (or criteria) other than polarization could be used. For
example, time division multiplexing could be used to switch between
the optical paths.
[0047] The pupil relay 33 is optional but enables larger distances
between the input ports 21, 22 on the waveguide 20. The pupil relay
33 may be constructed using any known or convenient method and
materials for transferring an image pupil from one location to
another. For example, the pupil relay 33 may be constructed from a
sequence of paraxial lenses that focus the pupil to an intermediate
image and then collimate it, followed by a mirror to redirect the
light into the corresponding input port of the waveguide. The
approach shown in FIG. 5, therefore, enables a single light engine
to provide two pupils for an image to two separate in-coupling
elements on a waveguide, without significantly increasing the cost
and size of the system, thereby greatly increasing the FOV with
current materials and manufacturing technologies.
[0048] FIGS. 6 and 7 illustrate another embodiment that uses
multiple input pupils on a waveguide, in which two (or more)
microdisplay imagers are combined in the same light engine.
Specifically, FIG. 6 schematically shows an example of certain
relevant components of the display module 54 for such an
embodiment. The view in FIG. 6 is from directly above the display
module 54, looking down.
[0049] As shown, the same illumination and imaging optics can be
used to produce two overlaying portions of an image, which can be
separated using, for example, a polarizing beam splitter (PBS). The
left and right portions of the image are initially separated within
the light engine 61 into p-polarized and s-polarized light,
respectively. Then, additional optics route these two portions of
the image to the appropriate output port 34 or 36 of the display
module 54, which are optically coupled to corresponding input ports
21 and 22, respectively, of the waveguide 20. Specifically, a PBS
62 in combination with a quarter-wave plate (retarder) 63 and
polarization mirror 64 cause the initially s-polarized right
portion of the image to be converted to p-polarized light that is
directed to the right output port 36 of the display module 54, and
from there, into the right input port 22 of the waveguide 20. Also,
the PBS 62 in combination with prism 65 causes the initially
p-polarized left portion of the image to be directed to the left
output port 34 of the display module 54, and from there, into the
left input port 21 of the waveguide 20. As with the approach
described above, pupil relay optics optionally can be used to
transfer any one or more of the pupils further away from the light
engine 61, to enable the input ports 21, 22 on the waveguide 20 to
be located relatively far away from each other (e.g., as shown in
FIGS. 4 and 5.
[0050] FIG. 7 schematically illustrates an example of certain
relevant components of the light engine 61 of FIG. 6, according to
certain embodiments. The view in FIG. 7 is from the right side of
the display module 54. Note that some embodiments may include other
active and/or passive components, not shown. The light engine 61 in
the illustrated embodiment includes at least one light source 71,
such as a color LED. Although only one light source 71 is shown in
FIG. 7, in practice there may be multiple light sources provided
for each eye of the user, e.g., one for each color component of
whatever color model is being employed (e.g., red, green and blue).
The same or a similar configuration as shown in FIG. 7 can be used
to combine light from such multiple light sources.
[0051] The light engine 61 further includes multiple imagers (e.g.,
LCOS microdisplays) 72A and 72B that generate separate portions of
an image intended for display to a particular eye of the user. The
two imagers 72A, 72B can be identical in size, functionality, etc.
A retarder (e.g., quarter-wave plate) can be placed before the
waveguide at one of the waveguide inputs to have optimum
polarization entering the waveguide.
[0052] Additionally, the light engine 61 includes a combination of
PBSs 74, 75, one or more reflective lenses 76 and one or more
quarter-wave plates 77, that generates the separate portions of the
image and propagates them simultaneously through the output port 78
of the light engine 61. More specifically, a first PBS 74 reflects
s-polarized light from the light source 71 upward to a first
microdisplay imager 72A, which generates one portion of the image.
The PBS 74 also causes p-polarized light from the light source 71
to be propagated straight through to the other microdisplay imager
72B, which produces a second portion of the image. Both portions of
the image (separately constituting s-polarized and p-polarized
light) then propagate downward through the PBS 74 to a second PBS
75, which directs them to birdbath-shaped reflective lenses 76 via
quarter-wave plates (retarders) 77. The image portions are then
reflected back by the reflective lenses 76 through the quarter-wave
plates 77 and then through the PBS 75. From there, the image
portions are output through the output port 78 of the light engine
61 and provided to additional optics in the display module 54, as
shown by the example in FIG. 6.
[0053] FIG. 8 illustrates an example of a method of using multiple
input pupils on a waveguide in an HMD device. The method begins at
step 801 with generating individually a plurality of different
portions of an image to be conveyed to an eye of the user of the
HMD device. Next, light representing each portion of the image is
coupled into a separate one of a plurality of optical input ports
of the waveguide at step 802. At step 803, the light representing
the multiple portions of the image is combined within the waveguide
to form light representing an integrated image. Light representing
the integrated image is then output from the waveguide to the eye
of the user at step 804.
[0054] In certain embodiments described above, a pupil relay (e.g.,
pupil relay 33 in FIG. 5) is used to spatially transfer the pupil
from one location to another. A pupil relay may also be desirable
for other purposes in an HMD device and/or in other types of
products or applications. Conventional pupil relay systems,
however, such as the Offner-type relay, tend to be very complex to
correct for aberrations in the system and to ensure that the
performance of the system does not degrade with that of the pupil
relay. With their relatively large size and weight, the design of
conventional pupil relays makes them poorly suited for use in HMD
systems and other near-eye display systems, and tolerances on such
systems are usually too sensitive to permit mass-production of any
included pupil relay in a cost-effective manner. To achieve a
low-cost, tolerance-insensitive pupil relay would be useful for
consumer electronics products with a need for multiple pupils or a
single spatially translated pupil in an optical system.
[0055] Introduced here, therefore, is a pupil relay that overcomes
the above-mentioned problems and is suitable for use in an HMD
device or other type of near-eye display device or system. The
pupil relay can be a waveguide with optical properties such that
the entry pupil and exit pupil of the waveguide have substantially
identical size and shape, and such that polychromatic light rays
input to the pupil relay propagate collinearly through the pupil
relay by TIR, so that the corresponding output light rays have
substantially identical chromatic properties to those of the input
light rays; that is, the pupil relay is achromatic. In this
context, "substantially identical" means that there is no
perceivable difference in these properties to a human user. The
waveguide pupil relay introduced in the following description can
be employed in an HMD device or other type of near-eye display
device, for example as pupil relay 33 in FIG. 5, and/or for other
purposes described herein.
[0056] Waveguides have traditionally been used to expand pupils
over a specific distance, but not to spatially translate a pupil
without modification. Furthermore, waveguides generally require
their parameters to be tuned to specific angles and wavelengths.
Additionally, waveguides traditionally have been used as pupil
expanders only for single colors, not for expanding (or spatially
translating) a multi-color pupil.
[0057] Conventionally, in waveguide-based optical elements such as
pupil expanders, light rays of different colors propagate at
different angles inside the substrate. A waveguide pupil relay such
as introduced here, however, enables rays of different colors to
propagate collinearly through the pupil relay, i.e., the pupil
relay is achromatic. Unlike traditional optics that focus the pupil
to an intermediate image plate then recollimate the light, a
waveguide pupil relay such as introduced here can propagate the
light through its length by TIR, resulting in the same pupil
characteristics at the waveguide's output as at the input. The
waveguide can be constructed by use of injection-molding according
to current manufacturing technique, for example, to produce a
faceted waveguide that achromatically relays the pupil.
[0058] In certain embodiments, an example of which is shown in FIG.
9A, a waveguide pupil relay 130 includes faceted (wedge-shaped)
input and output couplers 131 and 132 to correct for chromatic
displacements due to refraction. In particular, by incorporating a
thin triangular prism ("wedge") coupler 131, 132 at both the input
end and output end of the pupil relay 130, the waveguide pupil
relay 130 corrects for the different refraction angles of different
colors, e.g., red and green. Polychromatic light 145 is received
through an input pupil 138 at the input end of the waveguide pupil
relay 130 and is output at the output end via an exit pupil 139.
The exit pupil 139 has the same size, shape and chromatic
properties as the entry pupil 138. Note that while rays of only two
colors are illustrated, the same principle can be applied in
similar manner to propagate three or more colors through a
waveguide pupil relay. Since blue is mostly invisible to humans in
the periphery of the FOV, this very low-cost pupil relay can be
used in, for example, a dual-color (e.g., red-green) peripheral
vision system in an HMD and/or other applications where very high
quality imaging is unnecessary. In other applications, the
principles introduced here be used to produce a pupil relay that
spatially translates a pupil with three or more colors (e.g., red,
green and blue in an RGB color model) and/or in applications that
require high-quality imaging.
[0059] In the illustrated embodiment, the waveguide 130 includes a
substrate 133 that has a top surface 134 and a bottom surface 135
that are parallel to each other and that are internally reflective
so as to provide TIR of light rays propagating within the substrate
133. As shown in FIG. 9A and further illustrated in FIGS. 9B and
9C, the substrate 133 further has slanted light transmission
surfaces 136 and 137 at its input and output ends that are parallel
to each other but that are neither parallel nor perpendicular to
the top surface 134 and bottom surface 135. That is, the light
transmission surfaces 136 and 137 are oriented at oblique angles
relative to the top surface 134 and bottom surface 135 of the
substrate 133.
[0060] In addition to the substrate 133, the waveguide also
includes an input wedge coupler 131 (FIG. 9B) that has a surface
physically and optically coupled to the first light transmission
surface 136 of the substrate 133, and includes an output wedge
coupler 132 that has a surface physically and optically coupled to
the second light transmission surface 137 of the substrate 133. The
substrate 133 and the wedge couplers 131 and 132 can each be made
of a rigid, light-transmissive material, such as any of various
types of optical grade glass or plastic. In certain embodiments,
the substrate 133 is a single piece of such material. However, in
some embodiments, the wedge couplers 131 and 132 may be of
different material than the substrate 133 (e.g., one may be crown
glass while the other is flint glass), to facilitate the collinear
propagation of light, i.e., by taking advantage of their different
indices of refraction in applying Snell's law.
[0061] The input wedge coupler 131 has an outer surface 141 that is
the overall input surface of the waveguide 130, and has another
surface opposite to the input surface 141, that is physically and
optically coupled to the first light transmission surface 136 of
the substrate 133. The output wedge coupler 132 has an outer
surface 142 that is the overall output surface of the waveguide
130, and has another surface opposite to the output surface 142,
that is physically and optically coupled to the second light
transmission surface 137 of the substrate 133. The outer surfaces
of the input wedge 131 and the output wedge 132 (i.e., the input
surface 141 and the output surface 142 of the waveguide pupil relay
130) are each oriented at oblique angles relative to the top and
bottom surfaces 134, 135 of the substrate 133 and relative to the
first and second light transmission surfaces 136, 137 of the
substrate 133, as further illustrated in FIGS. 9B and 9C. In at
least some embodiments, the input wedge coupler 131 and the output
wedge coupler 132 are identical to each other in size, shape and
material, but have opposite orientations in the vertical axis when
integrated with the rest of the pupil relay 130. In other
embodiments, the input wedge coupler 131 and output wedge coupler
132 may be non-identical to each other in size, shape and/or
material.
[0062] The wedge couplers 131 and 132 can be used to achromatically
correct light propagation by decreasing the dispersion/angular
separation of multi-wavelength light refracted into the system. The
wedge couplers' internal angles .phi.1, .phi.2 and .phi.3 are
chosen as a function of the wavelengths to be propagated through
the pupil relay 130, and dispersion can be compensated with the
proper selection of materials based on their Abbe numbers and
partial dispersion ratios.
[0063] Referring to FIG. 9B, light rays containing multiple colors
(where different-type dashed lines each represent a different color
in the figures) initially strike the input surface 141 of the pupil
relay 130. With a desired internal propagation angle (collinear for
both colors), by application of Snell's law during the design
phase, one can appropriately select the indices of refraction of
the input wedge coupler 131 and the substrate 133 independently,
and can select the slant angle on each face of the wedge coupler
131, to separate the two (or more) colors in the input wedge
coupler 131 and then recombine them collinearly into the substrate
133. For example, the rays 151 and 152 of two (or more) different
colors (e.g., red and green) in polychromatic input light 145 are
refracted at the input surface 141 into the wedge coupler 131 at
different angles. In other words, light rays 151 of one color are
transmitted into the input wedge coupler 131 at one angle and light
rays 152 of another color are transmitted into the wedge coupler
131 at a different angle. However, the wedge coupler 131 can be
constructed to have specific angles and/or materials such that when
the light rays 151 and 152 strike the opposite surface of the wedge
coupler, i.e., the internal interface formed at surface 136, they
are again differently refracted, as a result of which the rays 151
and 152 are transmitted collinearly into the substrate 133 and
thereafter propagate collinearly through the substrate 133 by
TIR.
[0064] Similarly, referring now to FIG. 9C, at the output end of
the waveguide pupil relay 130, light rays 151 and 152 of different
colors propagating collinearly through the substrate 133 strike
internal interface formed by the joining of the substrate at
surface 137 to the output of wedge coupler 132. There the rays 151
and 152 are refracted at different angles into the output wedge
coupler 132, such that they are no longer propagating collinearly.
However, the angles and/or material of the output wedge coupler 132
are chosen such that upon exiting the output wedge coupler 132 at
the output surface 142, the rays 151 and 152 of different colors
are recombined and propagating collinearly. Consequently, the exit
pupil 139 has the same size and chromatic properties as the input
pupil 138.
[0065] In some embodiments, instead of (or in addition to) using
faceted ends, a waveguide pupil relay may include one or more DOEs
in conjunction with high index-of-refraction materials, to
collinearly propagate colors from different diffracted modes.
Examples of such an embodiment are shown in FIGS. 10 and 11. As
with the embodiment described above, these embodiments also
spatially translate the pupil so that the entry and exit pupils
have substantially identical size, shape and chromatic
properties.
[0066] In FIG. 10, instead of faceted ends, a waveguide pupil relay
150 includes two high-aspect-ratio surface relief diffraction
gratings 154 and 156 as DOEs (one on the input end and one on the
output end), formed as part of or proximate to a given surface 157
of the substrate of the pupil relay 150 (i.e., a surface parallel
to the direction of propagation of the light rays within the
substrate, shown as the top surface of the pupil relay 150 in FIG.
10). In this description, "proximate to" means no deeper than one
micrometer from the surface. It may be desirable to make the depth
of each DOE relatively large compared to its period. The DOEs 154
and 156 are designed to cause light rays of different colors to
propagate collinearly through the pupil relay substrate and to
continue to propagate collinearly upon exiting the pupil relay 150,
respectively. If the pupil relay 150 is formed by an injection
molding process, the DOEs 154 and 156 can be formed as part of or
after that injection molding process. For example, in various
embodiments, the DOEs 154 and 152 may be stamped into the surface
of the pupil relay 150 during or after the injection molding
process.
[0067] FIG. 11 shows another way of combining multiple colors into
a single waveguide by using diffraction gratings. In FIG. 11, the
pupil relay 160 includes at least four diffraction gratings 161
through 164 formed in or proximate to two opposite surfaces of the
substrate that are parallel to the direction of propagation of the
light rays within the substrate (shown as the top and bottom
surfaces of the pupil relay 160 in FIG. 11). The diffraction
gratings 161 and 162 on one surface (e.g., top surface) of the
pupil relay couple a first color, and the diffraction gratings 163
and 164 on the opposite surface (e.g., bottom surface) of the pupil
relay couple a second color. This can be done using, for example,
diffraction gratings that work only on one polarization (colors
have orthogonal polarizations) or using switchable diffraction
gratings to enable selection of the coupled color for each
diffraction gating. As mentioned above, the same principle can be
applied to allow collinear propagation of three or more colors
through the pupil relay in the embodiments of FIGS. 10 and 11.
[0068] In the embodiments of FIGS. 10 and 11, each of the DOEs 151,
152 161-164 can be part of a surface of the substrate of the pupil
relay, or can be buried within the substrate. Hence, the light
input surface and light output surface of the pupil relay 150 or
160, respectively, are each a DOE, or a portion of the substrate
surface directly over a DOE if the DOE is buried below the surface.
It can be assumed that each DOE in the pupil relay is substantially
coplanar with at least one of the surfaces of the substrate that
are parallel to the long axis of the pupil relay (i.e., each DOE is
parallel to such surface and within one micrometer of depth of such
surface).
[0069] In some embodiments, DOEs can be used in conjunction with
one or more faceted ends in a waveguide pupil relay. Hence, aspects
of the embodiments of FIGS. 10 and 11 can be combined with aspects
of the embodiments of FIGS. 9A, 9B and 9C. For example, one or more
DOE use could be formed in or proximate to the input surface and/or
output surface in the faceted and embodiment of FIGS. 9A, 9B and
9C.
[0070] As another example, and as shown in FIGS. 12 and 13, one or
more DOEs (e.g., diffraction gratings) can be positioned at
intermediate points along the waveguide to out-couple light of a
particular wavelength or wavelengths, such as to provide a tertiary
pupil. One or more such DOEs placed along the waveguide can
out-couple single or multiple colors at specific angles. FIG. 12
shows a faceted-end embodiment similar to that in FIG. 9A, but
further including a DOE 172 positioned intermediately along the
length of the substrate 133, for out-coupling light of a particular
color or colors. FIG. 13 shows a waveguide pupil relay 180 similar
to that shown in FIG. 10 but further including a DOE 176 positioned
intermediately along the length of the substrate, for out-coupling
light of a particular color or colors. A similar modification can
be made to the embodiment of FIG. 11.
Examples of Certain Embodiments
[0071] Certain embodiments of the technology introduced herein are
summarized in the following numbered examples:
[0072] 1. An optical waveguide comprising: a light-transmissive
substrate that includes a plurality of internally reflective
surfaces to enable light rays of a plurality of different colors to
propagate through the substrate by total internal reflection; an
input surface to input light rays of the plurality of different
colors through an entry pupil of the optical waveguide; and an
output surface to output light rays of the plurality of different
colors from the substrate through an exit pupil of the optical
waveguide, the optical waveguide having optical properties such
that the entry pupil and exit pupil have substantially identical
size and shape and such that the input light rays and output light
rays have substantially identical chromatic properties.
[0073] 2. The optical waveguide of example 1, wherein the substrate
is rigid.
[0074] 3. The optical waveguide of example 1 or example, the
optical waveguide having physical dimensions such that the optical
waveguide is suitable for use in a near-eye display device.
[0075] 4. The optical waveguide of any of examples 1 through 3, the
optical waveguide having optical characteristics such that the
light rays of the plurality of different colors propagate
collinearly through the waveguide substrate.
[0076] 5. The optical waveguide of any of examples 1 through 3, the
optical waveguide having optical characteristics such that the
light rays of at least some of the plurality of different colors
propagate non-collinearly through the waveguide substrate.
[0077] 6. The optical waveguide of any of examples 1 through 5,
wherein the plurality of different colors include at least three
colors of a primary color model.
[0078] 7. The optical waveguide of any of examples 1 through 6,
wherein at least one of the input surface or the output surface is
oriented at an oblique angle relative to the plurality of
internally reflective surfaces.
[0079] 8. The optical waveguide of any of examples 1 through 7,
wherein the input surface is oriented at an oblique angle relative
to the plurality of internally reflective surfaces.
[0080] 9. The optical waveguide of any of examples 1 through 8,
wherein each of the input surface and the output surface is
oriented at an oblique angle relative to the plurality of
internally reflective surfaces.
[0081] 10. The optical waveguide of any of examples 1 through 9,
wherein the optical waveguide comprises a first wedge-shaped prism
coupled to an input end of the substrate, and wherein the input
surface is a first surface of the first wedge-shaped prism.
[0082] 11. The optical waveguide of any of examples 1 through 10,
wherein: the input surface is oriented at a first oblique angle
relative to the plurality of internally reflective surfaces; and
the first wedge-shaped prism has a second surface oriented at a
second oblique angle relative to the plurality of internally
reflective surfaces, wherein the second oblique angle is different
from the first oblique angle.
[0083] 12. The optical waveguide of any of examples 1 through 11,
wherein the optical waveguide comprises a second wedge-shaped prism
coupled to an output end of the substrate, and wherein the output
surface is a first surface of the second wedge-shaped prism.
[0084] 13. The optical waveguide of any of examples 1 through 12,
wherein the substrate includes a plurality of internally reflective
surfaces to cause the light of the plurality of colors to propagate
through the substrate by total internal reflection, and wherein the
input surface and the output surface are each substantially
coplanar with at least one of the plurality of internally
reflective surfaces.
[0085] 14. The optical waveguide of any of examples 1 through 13,
comprising a diffraction element that is part of the substrate and
located on or proximate to the input surface to cause the light
rays of the plurality of different colors to propagate collinearly
through the substrate.
[0086] 15. The optical waveguide of any of examples 1 through 14,
comprising a diffraction element that is part of the substrate and
located on or proximate to the output surface to cause the light
rays of the plurality of different colors to be out-coupled
collinearly from the optical waveguide.
[0087] 16. The optical waveguide of any of examples 1 through 15,
comprising a diffraction element that is part of the substrate and
located on or proximate to a surface of the substrate between the
input surface and the output surface, the diffraction element
configured to cause light rays of at least one the plurality of
different colors to be out-coupled from the optical waveguide at an
intermediate location on the substrate between the input surface
and the output surface.
[0088] 17. The optical waveguide of any of examples 1 through 16,
comprising a plurality of diffraction elements that are part of the
substrate and located on or proximate to the input surface or the
output surface, each of the diffraction gratings being configured
to transmit light of a different color.
[0089] 18. The optical waveguide of any of examples 1 through 17,
wherein at least one the plurality of diffraction elements
comprises a plurality of stacked diffraction elements.
[0090] 19. A pupil relay comprising: a rigid, light-transmissive
waveguide capable of conveying light rays of a plurality of
different colors; and means for propagating the light rays of a
plurality of different colors through the waveguide such that an
exit pupil of the pupil relay has substantially identical size and
shape as an entry pupil of the pupil relay and such that light rays
input to the entry pupil and light rays output through the exit
pupil have substantially identical chromatic properties.
[0091] 20. A near-eye display device comprising: a light source; a
microdisplay imager optically coupled to receive light from the
light source; a first waveguide having an optical input port and an
optical output port, the optical output port being disposed to
output light to a light receptor of a user of the near-eye display
device; and a second waveguide optically coupled to convey the
light from the microdisplay imager to the input port of the first
waveguide, the second waveguide including a light-transmissive
substrate that includes a plurality of internally reflective
surfaces to enable light rays of a plurality of different colors to
propagate through the substrate by total internal reflection; an
input surface to input, through an entry pupil of the second
waveguide, input light rays of the plurality of different colors;
and an output surface to output light rays of the plurality of
different colors from the substrate through an exit pupil of the
optical waveguide, the second waveguide having optical properties
such that the entry pupil and exit pupil have substantially
identical size and shape and such that the input light rays and
output light rays have substantially identical chromatic
properties.
[0092] Any or all of the features and functions described above can
be combined with each other, except to the extent it may be
otherwise stated above or to the extent that any such embodiments
may be incompatible by virtue of their function or structure, as
will be apparent to persons of ordinary skill in the art. Unless
contrary to physical possibility, it is envisioned that (i) the
methods/steps described herein may be performed in any sequence
and/or in any combination, and that (ii) the components of
respective embodiments may be combined in any manner.
[0093] Although the subject matter has been described in language
specific to structural features and/or acts, it is to be understood
that the subject matter defined in the appended claims is not
necessarily limited to the specific features or acts described
above. Rather, the specific features and acts described above are
disclosed as examples of implementing the claims and other
equivalent features and acts are intended to be within the scope of
the claims.
* * * * *